I said something mean to somebody, I feel bad but they don't seem to care, how do I get over it?

Talk to them. Say you feel bad for saying that and that you hope they forgive you. Then move on. “Ha you lost” is the most minor thing. Neither of you will remember it a year from now, and if they “don’t seem to care”, then it is probably already forgotten on their end.

Just tell this person, hey, just wanted to say I’m sorry for what I said the other day, about losing the race.

Bringing it up will just make him relive it.
Instead, just find chances to say ordinary things.
Just saying hi when you see him should be enough to let him see you are not a jerk.

Since they don’t care, forget it & remember to NEVER do it again!!! Just remember how bad it has made you feel, so don’t ever utter those words again.

If you are feeling so badly, a quick apology will make you feel better. So do it and then be prepared to move on whatever their reaction is.

I think that’s the biggest punishment. If the person scolds or shows anger to us in return of our bad activities, it would be easy for us to move on from that bad situation. If not it will be bad to let go !!